Spectroscopic properties of Er3+ ions in LiNbO3 crystals codoped with HfO2

The results of the spectroscopic analysis of transition strengths for Er3+ ions in a series of Hf:Er:LiNbO3 crystals with variable Hf content and fixed Er content are reported. Unpolarized UV-VIS-NIR absorption spectra, upconversion fluorescence spectra excited at 800 nm, and microsecond time-resolved spectra excited at 400 nm and 800 nm by 800 nm femtosecond laser were measured at room temperature. The HfO2 incorporation has influence on Er3+ radiative lifetimes, and fluorescence branching ratios. For Hf(4 mol %):Er(1 mol %):LiNbO3, Ω2=2.63×10-20 cm2, Ω4=2.86×10-20 cm2, and Ω6=0.72×10-20 cm2. Ω2<Ω4 is contrary to the Er3+ general trend of Ω2>Ω4>Ω6 when the Hf content is below its threshold concentration. In addition, the sum of Ω increases with the Hf content when the HfO2 content below 6 mol % is unfamiliar. The upconversion mechanism is discussed in this work.